1. Field of the Invention
The present invention relates generally to a semiconductor process for forming gates with different pitches and different dimensions, and more specifically to a semiconductor process applying sidewall image transfer (SIT) techniques for forming gates with different pitches and different dimensions.
2. Description of the Prior Art
Field effect transistors are important electronic devices in the fabrication of integrated circuits, and as the size of the semiconductor devices becomes smaller and smaller, the fabrication of the transistors also has to improve and is constantly enhanced to fabricate transistors with smaller sizes and higher quality.
With the increasing miniaturization of the semiconductor devices, various multi-gate MOSFET devices have been developed. The multi-gate MOSFET is advantageous for the following reasons. First, the manufacturing processes of the multi-gate MOSFET devices can be integrated into the traditional logic device processes, and thus are more compatible. In addition, since the three-dimensional structure of the multi-gate MOSFET increases the overlapping area between the gate and the substrate, the channel region is controlled more effectively. This therefore reduces the drain-induced barrier lowering (DIBL) effect and the short channel effect. Moreover, the channel region is longer for the same gate length. Therefore, the current between the source and the drain is increased.
In another aspect, poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as the metal-oxide-semiconductor (MOS). With the trend towards scaling down the size of semiconductor devices, however, conventional poly-silicon gates face problems such as inferior performance due to boron penetration and unavoidable depletion effect. This increases equivalent thickness of the gate dielectric layer, reduces gate capacitance, and worsens a driving force of the devices. Therefore, work function metals that are suitable for use as the high-K gate dielectric layer are used to replace the conventional poly-silicon gate, which serves as a dummy gate first, to be the control electrode.
Accordingly, the multi-gate MOSFET devices advanced by integrating with work function metal gates have been attempted in modern industry.